Magnetic disk and its manufacturing method

ABSTRACT

In a thin film magnetic disk, a micro projections are formed on a substrate in a circumferential direction. A height of the micro projections is several nm to several tens of nm and a density of the micro projections is several hundred pcs/mm to several tens of thousands of pcs/mm 2 . With this arrangement, a magnetic disk fulfilling a head floating characteristic of a narrow space and further fulfilling a mechanical anti-sliding characteristic such as a contact start-stops characteristic and a head stickiness and the like is provided so that high reliability is attained. In the thin film magnetic disk, a bearing ratio curve of a sectional shape measured in a radial direction of the textured substrate has a bearing ratio of 0.1 to 10% at the surface layer (a cutting height of 5 to 10 nm). In this way, a pressure receiving area under a sliding of the magnetic head is increased.

This application is a Continuation of application Ser. No. 08/472,457,filed Jun. 7, 1995, abandoned, which is a Divisional Application of U.S.application Ser. No. 07/933,893, filed Aug. 24, 1992, which is acontinuation of application Ser. No. 07/224,360, filed Jul. 26, 1988,abandoned.

BACKGROUND OF THE INVENTION

This invention relates to the surface character of a thin film magneticdisk, and more particularly to a magnetic disk having a preferablesurface character with respect to a durability of the disk surface suchas head flyability, contact start-stops characteristic and headstickiness for a thin film magnetic disk.

In the conventional system, it has been found that as described inJapanese Patent Application Laid-Open No. 62-219227 a substrate havingmicro projections in a substrate for a thin film magnetic disk (asurface work for forming the micro projections is hereinafter referredto as texture) has surface uneveness with its maximum roughness of 0.02to 0.1 μm, and as shown in FIG. 10, a non-magnetic metallic layer 31 anda magnetic thin film medium 32 are formed on the substrate 1, resultingin that a coercive force of the thin magnetic film becomes more than 500Oe in the above-mentioned maximum surface roughness and so anon-magnetic metallic film (a chromium film) can be made thin to improveproductivity. As a result of a contact start-stop test, no scars havebeen found on the disk surface under twenty thousand times of testing.However, when the maximum surface roughness is more than 0.1 μm, a headcrush may easily occur and if no texture is applied, a scar may occur attimes over 5,000 times of a contact start-stop test and then the headcrush is generated.

As the conventional type of texture, as an example, as described in Jap.Pat. Laid-Open No. 54-23294, it employs a method and a disk workingdevice as illustrated in FIGS. 7, 8 and 12. In the drawings, 2designates a substrate relating to a disk, central lines of a pair ofcontact rollers 8 (both of them are made of resilient rubber) arearranged in a radial direction of this disk so as to hold this disk andthen a grinding tape 4 (4A and 4B) running upward and downward is placedbetween the contact roller 8 (8A and 8B) and the disk 2. Simultaneously,with a pressing of the contact roller and a rotation of the disk, thecontact roller 8 is reciprocated and slid in a radial direction, to makea simultaneous working of both surfaces of the disk. According to thistexture, it is possible to form micro projections without grindingunevenness. However, it shows a problem that a non-stable raising partis generated at the shoulder portions of the micro projections alongwith this formation and the raised portions are left as microprojections on the surface.

It is described that in the prior art, uneven surfaces with a maximumsurface roughness of 0.02 μm to 0.1 μm are formed on the surface of thesubstrate (texture), thereby even if a thickness of the non-magneticmetallic layer (chromium film) is made thin, a coerive force of themagnetic thin film medium (Co-Ni) is more than 500 Oe and it may fulfilla contact start-stop characteristic of twenty thousand times withoutgenerating any head crush. However, in the prior art, only the maximumsurface roughness is restricted or defined, and so if a texture forforming micro projections is applied to the substrate covered withaluminum alloy or anode oxidization aluminum or Ni-P plating or thelike, fine projections are generated on the shoulder portions of themicro projections. Due to the fine projections, if a floating test forthe head is carried out in a narrow clearance, for example, in a headfloating clearance of 0.2 μm, the head and the micro projections mayintermittently contact with each other, resulting in damaging a headfloating characteristic and causing a head crush. In addition, theupper-most surface of the disk is varied under a sliding movement of thehead in case of performing a test of contact start-stops, a disk surfaceis made smooth under this variation, a horizontal resistance applied tothe head is increased and this causes head crush. In view of this fact,it is important to define the micro projections under the texture and amere definition of the maximum surface roughness can not explain theeffects on disk start-stops or head crush. No consideration is made of ashape of projection or a repetition time from the mean surface ratherthan from the maximum surface roughness. In addition, no most importantproposal for the shape of the uneven surface of the substrate has beenidentified for improving the head crush or a start-stops characteristic.

In this specification, the micro projection designates a respectivemountain having a minute height in and located a pseudo circumferentialdirection of the disk or in respect to the texture formed helically asshown "A" in FIG. 31, as to the surface roughness curve being measuredin a radial direction of the disk from its central sine to the projecteddirection. A height of the micro projection designates a distancebetween a top of a respective mountain and the central line. In FIG. 31,a reference character B designates a curve of section and a referencecharacter C designates a center line, respectively.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a magnetic diskhaving a superior head floating characteristic and a high reliability bya method wherein a substrate having a Ni-P plating is worked withtexture for forming the most suitable surface character that is appliedin consideration of the sliding characteristics such as a head crushcause, a contact start-stops characteristic and a head stickiness andthe like.

In order to accomplish the above-described object, in the presentinvention for making a thin film magnetic disk, micro projections areformed on the substrate in its circumferential direction, a height ofeach micro projection is several nm to several tens nm and a density ofpresence of the micro projections is several hundred/mm² to several tensof thousands/mm². With this arrangement, the present invention canprovide a highly reliable magnetic disk fulfilling a head floatingcharacteristic in a narrow space and further fulfilling a mechanicalanti-sliding characteristic such as a contact start-stops characteristicor a head stickiness and the like.

In addition, the present invention provides a highly reliable thinmagnetic disk in which a bearing ratio curve for a sectional shapemeasured in a radial direction of the textured substrate has a surfaceexpressing a surface condition with a cutting length ratio of 0.1 to 10%at the surface layer (a cutting height is 5 to 10 nm) so that a pressurereceiving area caused by the sliding movement of the magnetic disk isincreased and thus its anti-sliding characteristic is improved.

Further, in respect to a simultaneous working of both surfaces of thesubstrate of the thin film magnetic disk, the surface of the substrateis worked while a first grinding tape is being oscillated in a radialdirection of the disk rotated under a desired pressing force and arelative speed and slid. Further, a second grinding tape havingparticles of a diameter smaller than that of the first grinding tape isapplied and the pressing force is made low and the relative speed ismade high. With this arrangement, the top portions of the microprojection on the worked surface are made flat and it is possible toprovide a substrate for a magnetic disk fulfilling various conditionsrequired for making an anti-sliding characteristic of the magnetic disksuch as a head floating characteristic, a contact start-stopscharacteristic and a head stickiness and the like.

Further, it is possible to provide the above-mentioned highly reliablemagnetic disk capable of forming uniform micro projections over anentire disk surface by an apparatus for working both surfaces of thedisk with grinding tapes comprising a pair of contact rollers installedat both sides of the disk pressing the grinding tapes against the disksurfaces with a desired minute pressing force; parallel leaf springs forsupporting the contact rollers and for applying a minute pressing forceto them; a pressure applying and moving means for moving the parallelleaf springs, adjusting influence of a back tension and the like causedby a taking-up of the grinding tapes and adding a minute pressing force;and a pressure measuring means fixed to the parallel leaf springs foruse in detecting the above-mentioned pressing force during rotation ofthe disk and reciprocating movement of the contact roller unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view for showing one preferred embodimentof a disk machining device of the present invention.

FIGS. 2a, 2b and 2c are a plan view and a top plan view for showing asubstantial part of the machining device, respectively.

FIG. 3 is a front elevational view for showing a detailed part of thedisk cleaning means shown in FIG. 1.

FIG. 4 is a side elevational view for showing this disk cleaning means.

FIG. 5 is an enlarged sectional curve for showing one example of a disksurface worked by a first machining head of the disk machining deviceshown in FIG. 1.

FIGS. 6 and 18 each show an enlarged sectional curve for showing oneexample of a disk surface machined with a second working head.

FIG. 7 is a front elevational view for showing a conventional type ofdisk machining device for forming micro projections.

FIG. 8 is a side elevational view for showing this device.

FIG. 9 is a sectional view for showing a thin film magnetic disk havingthe substrate of the present invention.

FIG. 10 is a sectional view for showing a prior art thin film magneticdisk.

FIG. 11 is an illustrative view for showing a sectional shape of a microprojection.

FIG. 12 is an illustrative view for showing a prior art disk machiningdevice.

FIGS. 13 and 14 show one example of a result of investigation of aheight of micro projection, a density and a characteristic of a magneticdisk, respectively.

FIGS. 15a and 15b are each a view for showing a minute variation in anano-meter order of the disk surface by measuring it with a highresolution SEM and expressing it with a variation of the sectional shapeof the surface.

FIG. 15a shows a sectional shape before a contact start-stops isperformed.

FIG. 15b shows a sectional shape after 20,000 times of a contactstart-stops operation.

FIG. 16 shows a bearing ratio curve A of a surface layer of the diskbefore a contact start-stops is performed, and also shows a bearingratio curve B after a bearing ratio curve is performed.

FIG. 17 shows a peak count distribution of the surface layer of thedisk, i.e., a density of the micro projection.

FIG. 19 shows a sectional view for showing a magnetic disk surface inwhich a magnetic film is formed on the disk shown in FIG. 6b.

FIG. 20 represents a characteristic of a contact start-stops and shows acomparison between the present invention indicated at C and the priorart indicated at D for a relation between the number of times of acontact start-stops cycle and head-friction.

FIG. 21 represents an output from a strain gauge showing a control overa minute pressing force of the present invention, wherein an influenceof a back tension caused by a taking-up of the grinding tapes isconsidered, an actual pressing force in case of working is detected andcontrolled accurately for a setting pressure force. In this figure, T₁designates an initial time, T₂ indicates a tape tension period, T₃ showsa pressing force adjusting period and T₄ indicates an actual machiningperiod.

FIGS. 22 and 23 show a result of investigation of a head floatingcharacteristic in respect to the magnetic disk before and after thepresent invention is applied, wherein FIG. 22 is a graph for showing anoutput of a piezo crystal head mounted on a floating magnetic head forthe case before the present invention is applied and FIG. 23 shows acase after the present invention is applied.

FIG. 24 shows a sectional structure for showing a prior art grindingtape.

FIG. 25 shows a sectional structure of a grinding tape of the presentinvention.

FIG. 26 shows a schematic view of a grinding tape dressing and truingdevice for use in making a grinding tape of the present invention.

FIGS. 27, 28, 29 and 30 illustrate a relation between the sectionalshape of a texture worked surface and a bearing ratio curve and alsoindicate a relation with a characteristic of contact start-stops.

FIG. 31 is an illustrative view for showing micro projections under asectional shape of the texture machining surface.

FIG. 32 is a view for illustrating a bearing ratio curve for expressinga nature of the sectional shape of the texture machining surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention has a feature that numerous mean micro projections areformed On a substrate for a magnetic disk, for example, an aluminumalloy, anode aluminum oxide, aluminum alloy coated with Ni-P plating andthe like, or on a substrate of glass or plastic.

In these micro projections, their shoulders are formed with raisedportions 36 as shown in FIG. 11 by forming the micro projection with adiamond byte or a cutting tool having micro grinding particles on thesurface of the substrate. A height of these micro projections is set inreference to a depth or a size of a groove 37 and a density of microprojection is set by a machining condition such as a density of microgrinding particles or a feeding distance of the tool and the like.

A requisite point required for a surface character of the magnetic diskconsists in fulfilling various characteristics of the magnetic disk suchas an electrical characteristic, a contact start-stops characteristicand a head stickness and the like without generating any head crush. Inthe magnetic disk, it is required that a super smooth surface of thedisk is attained for avoiding a crushing between the head and the diskdue to the fact that a head floating clearance becomes narrow foraccomplishing a high density. In turn, the head and the disk arecontacted with each other when they are stopped in order to reduce aprocessing time and so a so-called contact start-stops (hereinafterabbreviated to CSS) is performed to cause the head to be floated as thedisk is rotated. Due to this fact, in case that the disk surface has asmooth surface, i.e. a quite small surface roughness, the head and thedisk may generate a head stickiness due to the presence of lubricant ormoisture in the atmosphere on the disk when they are stopped, and so itposes a problem that an element for supporting the head or arm can bedamaged or its rotational driving can not be performed. In FIGS. 13 and14 illustrate results of an experiment performed by the inventors. Thesefigures show a relation between a height of micro projection, a densityand a head floating characteristic, a head stickiness through a texturework formed in the substrate (its details will be described later) byusing the grinding tape. In reference to these results, it is apparentthat there is a most suitable range of the surface layer for fulfillingtwo characteristics, a head floating characteristic and a headstickiness.

Further, the above-described surface character and a start-stopscharacteristic will be described in reference to the drawings.

FIG. 27 illustrates a sectional shape of a surface to which a texturework is applied and also to the substrate by using minute or finegrinding particles, where the micro projections are present with acertain disturbance. The bearing ratio curve of this sectional shapeshows a high gradient of bearing ratio curve as shown in FIG. 28 at arange where a bearing ratio is low, i.e. a range at A in FIG. 28. Whenthe magnetic head repeats a contact start-stops on the surface shown inFIG. 27, the micro projection has less contact with the head slidersurface and a pressure W/S (W: a head load, S: an actual contact areabetween the head slider and the disk surface) is increased, so thateither wear out or deformation is excessively produced and either amagnetic medium or a protective film having a thickness of about severaltens of nm on the substrate formed with the micro projections may haveremarkable damage. In turn, either wear out or deformation of the microprojections under a contact start-stops is excessively generated under arelation of σ<W/S and is reduced under a relation of σ≧W/S where σ is ayield strength at the micro projection part. Thus, the micro projectionis worn out or deformed, resulting in that an actual contact area isincreased to have an actual contact area S fulfilling theabove-described relation of σ<W/S and in this case if the magneticmedium or protective film is not damaged, but formed, a wearing-out ordeformation of the micro projection is almost eliminated and a stablesurface is exhibited.

Therefore, if the substrate shown in FIG. 27 is further machined at itssurface to form a trapezoidal shape having a smooth micro projection asshown in FIG. 29 and an actual contact area between the head slider andthe disk surface is increased to have a surface shape of an actualcontact area showing a relation of σ≧W/S at its initial condition, apressure at the micro projection is reduced, so that a wearing-out ordeformation of the micro projection under a contact start-stops iseliminated as a result, a magnetic disk having a stable and highlyreliable surface can be attained. The bearing ratio curve having asectional shape shown in FIG. 29 becomes one as shown in FIG. 30 and itshows that a gradient of the bearing ratio curve at the surface layer isquite low as shown in FIG. 30A.

Experiments performed by the present inventors show that a prior arttexture worked surface having the sectional shape as shown in FIG. 27has a bearing ratio curve, as its one example, with a bearing ratio at 5nm to 10 nm from the top part of the sectional curve, i.e. at a depthbelow the highest peak of 5 nm to 10 nm, the bearing ratio is 0.1% orless and in case of the magnetic disk using such substrate, a head crushwas generated at 2,000 times or less of a contact start-stops operation.Further, in case of the magnetic disk using the substrate having asurface as shown in FIG. 29 in which the texture work of the presentinvention is performed in two-stages, i.e. a surface of a bearing ratiocurve with a bearing ratio at a depth below the highest peak of 5 nm to10 nm being 0.1 to 10%, both the magnetic medium and the protective filmmaintain each of the functions at 20000 times or more of the time of acontact start-stops operation and kept the stable surface condition.

Further, the inventors surveyed a detailed variation of the magneticdisk surface after a contact start-stops operation. Experimentsperformed by the present inventors show that a top of the microprojection at its initial condition is made smooth under a repetition ofthe sliding movement of the magnetic head. The surface shape measuredfrom SEM observation for the disk surface tested in a contactstart-stops operation is shown in FIGS. 15a and 15b. The surface of thesubstrate having a contact start-stops testing in respect to the texturesubstrate and from a bearing ratio curve for the disk surface shown inFIG. 16 (a detailed description will be described later) and further thenumber of micro projections contacted with the head and the disk isincreased. For example, variation at the surface at 20000 times of astart-stops operation is made such that as shown in A of FIG. 15b amicro projection is varied by a height of 5 to 10 nm from its top partin its initial condition under a contact of the magnetic head with theslider surface, and when the micro projection is varied from the peakcount distribution curve at the disk surface under a condition shown inFIG. 17 by 5 to 10 nm from its top part of initial condition, the numberof micro projections contacting the magnetic head was severalhundred/mm² to several tens of thousand/mm². That is, when the height ofthe micro projection is more than several tens of nm, a floatingcharacteristic of the magnetic head is deteriorated to cause a headcrush to occur, and even if the micro projection is less than severaltens of nm, in the case of less density, the number of substratessupporting a head load under a sliding movement of the head under acontact start-stops test, i.e. the number of micro projections isreduced, they are made smooth immediately together with the number ofcontact start-stops, and thus an increased head friction causes the headcrush to be easily performed.

If the number of micro projections is less, a pressure of the microprojection receiving a head load is increased, so that the microprojection may easily be reduced or worn out, the lubricant layer orprotective layer of several nm formed on the substrate surface mayeasily be damaged. In case that the density of the micro projections ismore than several tens of thousands/mm² and a density is high, a lessvariation of the micro projection on the substrate is found due to themagnetic head. However, its contact area is increased, so that the headstickiness is easily generated under influence of a lubricant agent ormoisture in the atmosphere, a sliding resistance of the magnetic head incase of performing a contact start-stops is increased, and an elementfor the magnetic head or arm is easily broken or the disk is made hardto rotate.

The bearing ratio curve will be described in detail. This bearing ratiocurve is called an Abbott-Firestone (or bearing ratio) curve, and ingeneral, it is used for evaluating the sliding characteristic of abearing and the like. This bearing ratio curve, as shown in FIG. 32,shows a curve in which a sectional curve is cut from a top part of thesectional curve at a specified interval with respect to a referencelength E of the surface sectional curve (or surface roughness curve) anda total of each of cut lengths of the the sectional curve with thiscutting line is divided by the reference length E and this is expressedby a percentage for every cutting line. At the top part of the sectionalcurve, a cutting length determined by the cutting line is small and abearing ratio is low. That is, if there is a sliding element on thissurface, the sliding part is supported only by the top part of thesectional curve at the beginning of the sliding movement, so that apressure receiving area is small, a surface pressure is high, resultingin that the top part is frictionally engaged by the sliding element anda wearing-out or a deformation can easily be generated. Therefore, inthe case of a surface having a high bearing ratio at the top part of thesectional curve, i.e. a surface expressing a surface shape having a lowgradient of the bearing curve in a range of low bearing ratio in thebearing ratio curve, a pressure receiving area is higher at its initialcondition and a surface pressure of the micro projection supporting thesliding element becomes low, so that an anti-sliding characteristic isimproved. In this way, the bearing ratio curve is one of the evaluationmeans for expressing a load capacity with respect to the sectional curveof a surface slidingly supporting to the sliding element.

Therefore, for the surface character of the textured substrate, it isperferable to have a surface formed with uniform micro projections witha density of the micro projections being several hundred/mm² to severaltens of thousands/mm² as well as to have a height of the microprojections several nm to several tens of nm in view of theabove-mentioned result in reference to the floating characteristic ofthe head, a head load and a surface variation caused of a friction wearby the head sliding movement.

In view of the above, the most suitable surface for the magnetic disksubstrate is one in which as shown in FIG. 6, micro projections areformed in a circumferential direction, in a pseudo-manner in thesubstrate surface, that is, a sectional shape of the textured substratesurface has micro projections of a height of several nm to several tensof nm and a density on the substrate surface of several hundred/mm² toseveral tens of thousands/mm².

As a method for getting a substrate having such a surface character,there are various methods. As one method, for example, fixed grindingparticles such as grinding tape as disclosed in Jap. Pat. Laid-Open No.54-23294 are used and as shown in FIG. 1. The working head isreciprocated and slid in a radial direction of the substrate in respectto the mirror surface substrate in advance and a circumferential microporjection is formed in a pseudo-manner, and then micro raised portionsgenerated at the shoulders of the projections are controlled in a rangefrom several nm to several tens of nm. Further, the substrate is rotatedat a high speed from its light load with a grinding tape having moreminute particles than that of the above-mentioned grinding tape, wherebythe height of the above-mentioned micro projections is made uniform. Adensity of the micro projection can be varied optionally by varying adegree of particles of the grinding tape and controlling the number ofoperating grinding particles.

Several uniform micro projections having a height of the microprojection formed on the magnetic disk substrate of several nm toseveral tens of nm and having a density of several hundred/mm² toseveral tens of thousands/mm² are contacted with the slider surface ofthe head to receive the head load when the magnetic head is in a contactstart-stops condition. They hold the lubricating film coated on themagnetic disk surface and at the same time prevent an adhering of themagnetic head. Further, since several micro projections are contactedwith the head slider surface, a pressure of each of the microprojections is reduced, resulting in that a variation of the microprojections caused by a repetition of a contact start-stops operation,i.e. a deformation or wear-out is reduced and the surface character ofthe initial condition is kept. In addition, a height of the microprojection is several nm to several tens of nm and is quite short ascompared with a floating clearance of the magnetic head (a clearancebetween the magnetic head and the magnetic disk surface under a normalcondition) of 150 to 250 nm. Thus, the magnetic head may float with asufficient surplus in reference to an accuracy of assembly, an accuracyof rotation of the magnetic disk and a floating variation of themagnetic head and then the head crush caused by the striking of themagnetic head may not be generated.

Therefore, there is scarcely found a wearing-out or damage of theprotective film or lubrication film having a thickness of several nmformed on the magnetic disk surface. Further, a head stickiness is notgenerated. Also, an increasing of the head friction caused by arepetition of a contact start-stops is not found, and thus a magneticdisk which has a highly reliable head floating characteristic and afavorable anti-sliding characteristic can be provided.

Referring now to the drawings, one preferred embodiment of the presentinvention will be described. The present invention is an Al disk whichis made by a method wherein the disk is coated with a Ni-P plating of athickness of 10 μm, the disk is smoothly ground to a surface roughnessless than 2 to 3 nmRa, a projection shape is ground by grinding tapes asshown in FIG. 18 (a surface roughness meter step is applied to have asectional shape measured in an orthogonal direction to the projectionwith a needle shape of 0.1×2.5 μm), a height of the micro projectionmeasured at the shoulder part thereof is uniform in a range from severalnm to several tens of nm, a density is set to be 2000 to 3000 pcs/mm²,and an inner diameter of 40 mm and an outer diameter of 130 mm are set.Non-magnetic metallic film 31 of Cr system having a thickness of about500 nm as shown in FIG. 10 and a magnetic medium 32 of Co-Ni systemhaving a thickness of about 60 nm are sputtered onto the substrate so asto form a carbon protective film 33 and a lubrication film 34 having athickness of about 50 nm.

A surface shape of the magnetic disk thus formed is substantially thesame as the shape on the substrate described above as shown in FIG. 19,the surface roughness is 5.5 nmRa (5.3 nmRa on the substrate), a maximumheight of the micro projection in a predetermined spacing is 19 nm (20nm on the substrate) and a density is also substantially the same asthat of the former one.

As a result of a floating test at a head floating clearance of 0.2 μmwith respect to the magnetic disk, a contact between the head and thedisk surface is not detected, a superior floating characteristic isindicated, a variation of the magnetic disk surface shape caused by thecontact start-stops times is scarcely found, and as shown in FIG. 20, anincreasing of the head friction caused by the times of contactstart-stops is scarcely made, a problem of the head stickiness is notgenerated and thus a reliability of the magnetic disk is substantiallyimproved.

As an example of comparison, in the case of a magnetic disk having asectional shape as shown in FIG. 5 and having a micro projection on thesubstrate according to the prior art, a head friction is increased alongwith the time of the contact start-stops and a problem of damaging themagnetic head and a head crush occurs. It is apparent that the sectionalshape of the disk surface is remarkably varied by the contactstart-stops operation as compared with that of the present invention.

One of the manufacturing methods for the above-described substrate willbe described in detail in reference to FIG. 1.

A non-electrolyte Ni-P plating is formed to have a thickness of 10 um onboth surfaces of an Al disk. The surfaces are smoothly ground to asurface roughness less than 0.01 μmR_(max) and are worked with grindingtapes having alumina particles of #3000 particle size to form a microprojection in the Ni-P plated substrate.

This surface working method is performed such that as disclosed in Jap.Pat. Laid-Open No. 54-23294 the grinding tapes are pushed against bothsurfaces of the substrate shown in FIG. 12 with contact rollers, thegrinding tapes are reciprocated on the substrate while the substrate isbeing rotated and the grinding tapes are taken up in such a way as thegrinding tapes are slid on the entire substrate so as to formpseudo-circumferential or helical micro projections in both surfaces ofthe substrate. The most important point to be taken in case of formingthe micro projections is that a pressing force is added to the workinggrinding tapes that is highly accurately controlled in order to formuniform micro projections on the substrate. As a variable component ofthe pressing force, there is an influence of the back tension caused bya taking-up of the grinding tapes or a variation in the pressing forcecaused by a shape of corrugation in a circumferential direction of thedisk or a radial warp and the like. Then, as pressing means for thecontact rollers applying a minute force, parallel leaf springs areapplied, and there are provided a pressing and moving means for movingthe parallel leaf springs in a pressing direction, (piezo-electricactuator), a pressing force measuring means attached to the parallelleaf springs (a semiconductor strain gauge) and a control device forcontrolling the above-mentioned pressing and moving means in response toan output from the pressing force measuring means.

FIG. 21 is an output waveform caused by the pressing force measuringmeans composed of strain gauges 12 and 13 shown in FIGS. 2a and 2b incase that the working is carried with a set pressing force of 7.5N.Although the output by the pressing pressure measuring means shows 10.5Nat both surfaces of the disk, i.e. 12 and 13 in case of working, a backtension 3N caused by the taking-up of the grinding tapes and a variationof the pressing force caused by a shape of substrate, for example, acorrugation in a circumferential direction or a warp in a radialdirection of the substrate is controlled by a piezoelectric actuator, anactual pressing force during the machining operation is controlled tohave a value of 7.5N±1N. With this arrangement, a sectional shape of themicro projection is made such that a height of the micro projection froma mean surface is 20 to 30 nm and a density of occurrence i.e. a densityof a substrate surface of the micro projection can be controlled to thesurface character of about 3000 pcs/mm².

Then, several abnormal micro projections more than a height of 100 nmare generated at the substrate surface character and in particular, atthe shoulder of the deep projections and this causes a deterioration andan accident of head crush. Due to this fact, as shown in FIG. 1, thesurface was worked in the same manner as that of the first stage byusing the grinding tape of which the grain size is smaller than that ofthe above-described first stage. As a result of the second stage surfaceworking, a height of the abnormal micro projections was reduced, severaltop portions of the micro projections were made smooth and then thesurface having a sectional shape as shown in FIG. 6 could be formed. Inorder to remove a stain in the disk surface caused by working scaleswith the first surface working, means for cleaning the disk surface isarranged between the first stage and the second stage.

A constitution of the disk machining device for accomplishing theabove-described working means will be described in detail in referenceto the drawings.

FIG. 1 is a front elevational view for illustrating one preferredembodiment of a disk machining device for use in texture machining ofthe present invention. FIGS. 2a, 2b and 2c are a top plan view forshowing a substantial part of the device. FIG. 3 is a front elevationalview for showing a detailed part of a disk cleaning means shown inFIG. 1. FIG. 4 is a side elevational view for showing this disk cleaningmeans.

At first, an overall arrangement of the disk working device is describedin reference to FIG. 1. This device is comprised of a disk supportingmeans 1 capable of rotatably supporting a disk 2 of a workpiece; a setof contact roller units C capable of pressing the first grinding tape 4with a pressing force against both surfaces of the disk 2simultaneously; tape taking-up motors 7a and 7b for use in taking up thefirst grinding tape; an oscillating means W capable of oscillating thecontact roller units C in a radial direction of the disk 2; areciprocating means R capable of reciprocating the contact roller unitsC in a radial direction of the disk 2; a pair of working heads includinga first working head having a reciprocating means R capable ofreciprocating the contact roller unit C in a radial direction of thedisk 2 and arranged at one side of the disk supporting means and asecond working head H2 having the same constitution as that of the firstworking head H1, arranged at an opposite side of the first working headH1 with respect to the disk supporting means and having a second workinghead H2 having a second grinding tape with its particle diameter lowerthan that of the first grinding tape installed in place of the firstgrinding tapes. The device further has disk driving motor associatedwith a disk rotating means capable of rotating disk 2 in such a way as arelative speed between said first and second grinding tapes becomes adesired value; a disk cleaning means S arranged between both workingheads and capable of cleaning the disk; and a control device 17 capableof controlling both working heads H1 and H2, the disk driving motor 3and the disk cleaning means S.

Further, the above-mentioned working heads will be described in detail.In FIGS. 2a, 2b and 2c, the working head H1 is provided with a pair ofparallel leaf springs 10 and 11 movably supported in reciprocating meansR in an axial direction of disk 2; a pressing and moving means 23 foruse in moving the parallel leaf springs 10 and 11, eliminating aninfluence of back tension caused by taking-up of the grinding tapes 4aand 4b and capable of setting a desired low pressing force; a pressingforce correcting means 50 for making an efficient correction of avariation of minute pressing force under an infleunce of an accuracy ofthe disk shape when the disk is worked (for example, a piezo-electricactuator and the like); contact rollers 8 and 9 fixed to parallel leafsprings 10 and 11, arranged at both sides of the disk and having theircentral axes attached in a radial direction of the disk 2; a grindingtape driving device 7 attached to the reciprocating means R and slidingsaid grinding tapes 4 between the disk and the contact rollers; stressmeasuring means 12 attached to the parallel leaf springs 10 and 11; anda control means 17 for controlling the pressing and moving means 23 andthe pressing correcting means in response to an output from the stressmeasuring means.

Therefore, in the disk working device, the pressing force is varied inresponse to a variation of back tension caused by a taking-up of thegrinding tape which is a cause of a minute variation of a pressingforce, i.e. a diameter of each of the grinding tapes wound around asupply reel and a take-up reel is varied as the working proceeds, and atension force of the tape is applied. If the variation value is alwaysmeasured by the stress measuring means 12 and the parallel leaf springs10 and 11 are adjusted by the pressing and moving means 23, the pressingforce of the contact rollers 8 and 9 against the disk 2 can be keptconstant irrespective of the variation of the tension force of thegrinding tapes. In regard to a corrugation of the disk in acircumferential direction or a variation of a pressing force causedunder a warp of the disk in a radial direction when a working isperformed, it is possible to provide a correction of minute pressingforce under a better response by a pressing force correcting means 50such as a piezo-electric actuator and the like in order to improve aresponse of the correction of the pressing force. With theabove-mentioned function, an accurate forming of the micro projectionscan be performed.

The first working head H1 is arranged at one side of the disk supportingmeans 1 (a right side in FIG. 1) and is applied for forming microprojections (for example, a micro projection of a depth of about 0.04μm) at both surfaces of the disk 2. This working head H1 is comprised ofa tape taking-up motor 7a for use in taking up from lower to upperdirection the first grinding tape wound around each of a set of twocontact roller units C arranged at both side surfaces of the disk 2; anoscillating means W capable of oscillating the contact roller units C ina radial direction; and a reciprocating means R capable of reciprocatingthe units in a radial direction. Each of the contact roller units C iscomposed of a contact roller 8 used for pressing the first grinding tape4 against the disk 2 and of a pressing motor 14 capable of applying adesired pressing force to the contact roller 8 through the parallel leafsprings 10. To the parallel leaf springs 10 is attached a strain gauge12 for use in detecting a pressing force. The pressing motor 14 canapply a pressing force to the parallel leaf springs 10 by displacingthem in a direction orthogonal to the two surface of the disk. Thepressing force correcting piezo-electric actuater 50 can make acorrection of better response for the minute variation of the pressingforce during the working operation. The oscillating means W is comprisedof an oscillating motor 16, and a crank 55 for connecting the shaft ofthe oscillating motor 16 with the first working head H1. Thereciprocating means R may threadably transmit a rotation of thereciprocating motor 15 to the first working head Ill so as toreciprocate the working head.

The second working head H2 has, as described above, the sameconstitution as that of the first working head except for theinstallation at the second grinding tape in place of the first grindingtape. The second head H2 is arranged at the other side (left side inFIG. 1) of the disk supporting means and is used for removing the raisedportions of the micro projection formed on both surfaces of the diskwith the first working head.

A constitution of the working head will be described with detail inreference to FIGS. 2a and 2b.

Reference numeral 1 designates a disk mounting rotary shaft installedhorizontally, 2 a disk acting as a workpiece, 3 a driving motor for usein rotating a rotary shaft, 21 a rotatably supported screw, 15 areciprocating and moving motor for use in rotating the screw 21.Reference number 22 denotes a reciprocating and moving block supportedmovably in a radial direction of the disk, i.e. a direction of arrow A,having an internal thread threadably engaged with the screw 21, and areciprocating and moving means R is constituted by the screw 21 and themotor 15. Reference number 23 designates a moving body movably supportedin the reciprocating and moving block 22 in a direction of arrow A, 16indicates a vibrating device fixed to the reciprocating and moving block22 and the moving body 23 is vibrated by the vibrator device 16 with aminute amplitude. Reference number 24 shows a screw rotatably supportedby the moving body 23, 14 denotes a pressing motor for rotating thescrew 24, 10 and 11 denote a pair of parallel leaf springs movablysupported in an axial direction of the disk 2 in the moving body 23,i.e. in a direction of arrow B. A internal thread is made at thesupporting block 51 of the parallel leaf springs 10 and 11. Its internalthread is threadably engaged with the screw 24 and the pressing andmoving means is constructed by the screw 24 and the motor 14. In casethat a poor corrugation in a circumferential direction of the disk or apoor warp in a radial direction is found, a variation in pressing forceis generated when a working operation is performed. Due to this fact,the parallel leaf springs 10 and 11 are constructed such that aninternal thread is formed in a supporting block 51 provided with apressing force correcting piezo-electric actuater 50 and then it is slidin a direction B (for adding the pressing force). On the supportingblock 51 is mounted a reciprocating block 52 for moving the parallelleaf springs in a direction B through a piezo-electric actuater formoving it by a minute amount. Reference numbers 8 and 9 denote contactrollers rotatably arranged in the parallel leaf springs 10 and 11. Thecontact rollers 8 and 9 are arranged at both sides of the disk 2 andtheir central axes are directed toward a radial direction of the disk.Reference numbers 18a and 18b denote braking torque motors fixed to themoving body 23, 5a and 5b denote supply reels fixed to the output shaftsof the motors 18a and 18b, 7a and 7b designate taking-up motors fixed tothe moving body 23, 6a and 6b denote taking-up reels fixed to the motors7a and 7b, 4a and 4b indicate grinding tapes having fine grindingparticles such as diamond grinding particles or aluminum grindingparticles adhered and held on the substrate such as polyester film withresin as a binder. Both ends of the grinding tapes 4a and 4b are fixedto the supply reels 5a and 5b and take-up reels 6a and 6b. The grindingtape driving device is comprised of the motors 18a and 18b, supply reels5a and 5b motors 7a and 7b, take-up reels 6a and 6b, and the grindingtapes 4a and 4b which are passed between the disk and the contactroller. Reference numbers 12 and 13 denote strain gauges fixed to theparallel leaf springs 10 and 11, a reference numeral 17 denotes acontrol device for controlling motors 3, 14 and 15 and the like. Thecontrol device 17 controls the motor 14 and the pressing forcecorrecting piezo-electric actuater in response to the outputs from thestrain gauges 12 and 13 so as to move the parallel leaf springs 10 and11.

The disk cleaning means is comprised of rotary scrubbers (made of brushor sponge) for making a simultaneous cleaning of both surfaces of thedisk, a scrubber driving motor for rotating these rotary scrubbers, aircylinders (not shown) capable of reciprocating the rotary scrubbersbetween their dotted line position and solid line position and a liquidtank.

A reference numeral 60 indicated in FIGS. 1, 3 and 4 and the likedesignates a supplying part for supplying working liquid and cleaningliquid.

One preferred embodiment of texture work according to the disk workingdevice constructed as above and the preferred embodiment of magneticdisk characteristic in respect to the magnetic disk using the texturedsubstrate will be described.

At first, a method for texture working will be described. The disk isfixed to the disk supporting means. To the control device are setworking conditions such as a first pressing force, a relative speed, avibrating amplitude and a reciprocating time and the like.

In this case, when the disk working device is turned on, the disk isrotated by the motor 3 and at the same time the first working head isoscillated at a set oscillating amplitude by the oscillating motor, thegrinding tapes 4a and 4b are taken up with a specified force by thegrinding tape driving device, the pressing force for the disk isadjusted in such a way as its value becomes the first set pressingforce, and if the reciprocating and moving block 22 is reciprocated andmoved by the reciprocating and moving means R, the micro projection isformed in the surface of the disk 2 with the grinding tapes 4a and 4b.During this period, the speed of rotation of the disk 2 is adjusted insuch a way that the relative speed between the disk 2 and the firstgrinding tape 4 becomes the first set relative speed. In this way, whilethe working is promoted, working liquid is continuously supplied fromthe supplying part 60 to the disk. Then, even if the tensions of thegrinding tapes 4a and 4b are varied and the parallel leaf springs 10 and11 are deformed, the control device 17 may control the motor 14 inresponse to the outputs from the strain gauges 12 and 13, i.e. an amountof deformation of the parallel leaf springs 10 and 11, so that theparallel leaf springs 10 and 11 enable the pressing force of the contactrollers 8 and 9 against the disk 2 to be kept constant irrespective ofthe variation of the tension forces of the grinding tapes 4a and 4b inresponse to its amount of deformation. Thus, a minute pressing force canalways be kept, resulting in that small and uniform micro projectionscan be made. Further, as regards the variation of the pressing forcecaused by the rotation of the disk 2 and as regards the variation of thepressing force under a sliding movement of the working head toward theradial direction of the disk 2, the pressing force is varied under thecorrugation in a circumferential direction of the disk 2 or a rightangleness in a radial direction or an influence of warp. Thesevariations can be corrected immediately by the pressing force correctingpiezo-electric actuator 50 under an instruction of the control device17.

When the first working head is reciprocated by the desired times, thisworking head is retracted (is moved rightward as viewed in FIG. 1) andthen a supplying of working liquid is terminated.

Then, the rotary scrubber 61 placed at the broken line position 61' inFIG. 3 is lifted up to the solid line position (present position) andthis rotary scrubber 61 is rotated by the scrubber driving motor. Thedisk 2 is also rotated and the cleaning liquid is supplied from thesupplying part 60, and the disk 2 is cleaned. Upon completion of thiscleaning operation, the rotary scrubber 61 descends down to the brokenline position and then the supplying of cleaning liquid is terminated.

Then, the second working head 112 is promoted forward, the disk 2 isworked in the same manner as that of the first working head H1 by thisworking head.

That is, simultaneously with a rotation of the disk 2 by the motor 3,the second working head H2 is oscillated by the oscillating motor with adesired oscillating amplitude, the grinding tapes 62a and 62b are takenup under a specified force by the grinding tape driving device, apressing force against the disk is adjusted in such a way as it maybecome the second set pressing force. If the reciprocating and movingblock 63 is reciprocated and moved by the reciprocating and movingmeans, micro projections present on the surface of the disk 2 areremoved by the grinding tapes 62a and 62b and made smooth. During thisperiod, the speed of rotation of the disk 2 is adjusted by the diskdriving motor 3 in such a way that the relative speed between the disk 2and the second grinding tape may become the second set pressing force.In this way, the working liquid is continuously supplied from thesupplying part 60 to the disk while the working proceeds.

When the second working head H2 is reciprocated by the set number oftimes, the working head is retracted (in a leftward direction as viewedin FIG. 1) and the supplying of the working liquid is terminated.

Lastly, in the same manner as described above, the disk 2 is cleaned bythe disk cleaning means 64 and the disk working device is turned off.

If the disk 2 is removed from the disk supporting means 1, the desiredmicro projection is formed. Further, if a magnetic medium, a protectivefilm and a lubricant film are formed, it is possible to get the magneticdisk which is superior in an anti-sliding characteristic.

Then, a practical example of the present invention will be described.

A practical example in which a micro projection is formed on the disk 2having Ni-P plated on an Al disk with a thickness of about 10 um will bedescribed in reference to FIGS. 5 and 6.

FIG. 5 is an enlarged sectional curve for showing one example of surfacecharacter of the disk worked by the first working head of the diskworking device shown in FIG. 1. FIG. 6 is an enlarged sectional curvefor showing one example of the surface character of the disk worked withthe second working head.

The first grinding tape is operated such that the disk 2 is worked withthe first working head H1 while water soluble cutting liquid is beingsupplied with grinding particles of Al₂ O₃ having a particle diameter of3 μm, a first pressing force being 4N, a first relative speed being 4m/sec and an oscillating amplitude being 1 mm. As a result, microprojection having a depth V of about 40 nm was formed as shown in FIG. 5in the surface of the disk 2, the raised height of about 30 nm (microprojection) H was present and a raised ratio had a relation of H/V>5.The raised height showed a certain disturbance.

The second grinding tape was operated such that it has Al₂ O₃ grindingparticles having a particle diameter of 0.5 μm, with the second pressingforce being 2N, the second relative speed being 8 m/sec and anoscillating amplitude being 1 mm. The disk cleaned with pure water wasworked by the second working head H2 while water soluble cutting liquidwas supplied. The surface of the disk 2 had a depth of the microprojections V kept at about 40 nm as shown in FIG. 6, a raised heightwas decreased less than about 10 nm, a low disturbance was, a raisedratio H/V of about 0.25 thus, the desired micro projections wereattained.

According to the above-described preferred embodiment, since only theraised portions generated at the shoulder portions of the microprojections were tried to be removed by the first working head, it hasan effect that a micro projection depth V is 20 to 100 nm, a raisedheight (micro projection) H has a relation of H/V≦0.5 which enables asmooth surface having this ratio to be provided. Further, any kind ofmicro projection can be formed if the degree of grain or grindingparticle quality of the grinding tape, the times of reciprocating andsliding movement on the disk and a pressing force and other workingconditions are varied.

Under application of this method, the thin film magnetic disk 2 appliedas a substrate as shown in FIG. 9 having a non-magnetic metallic film31, a magnetic medium film 32, a carbon protective film 33 and alubricant film 34 on the substrate 30 has a superior head floatingcharacteristic, and a remarkable reliability and stability.

Various characteristics of the thin film magnetic disk formed with microprojections of the present invention will be described in detailtogether with an example of comparison. That is, the followingdescription will show a comparison between the disk having a height ofthe micro projections being several nm to several tens of nm and adensity of the micro projections being several hundred pcs/nm² toseveral tens of thousand pcs/mm.

In FIGS. 13 and 14 are shown results of surveying an influence of thehead floating characteristic and a head stickiness and another influenceon a deformation amount of surface character (micro projection) under acontact start-stops test as well as an influence of head friction withrespect to the thin film magnetic disk. The disk is formed by varyingvarious working conditions such as a degree of grinding particle of agrinding tape, the times of reciprocating of the working head and apressing force and the like to perform a texture on the surface, and byforming a non-magnetic metallic film, a magnetic medium film, a carbonprotective film and a lubricant film which are similar to the formercase and are formed on the substrate having a different height of microprojections and a varied density. In case that a height of the microprojections is less than several nm (2 to 3 nm), for example, or asubstrate which is approximately a polished surface, the surface had asuperior head floating characteristic. However, its head friction wasincreased, a problem of head stickiness was generated, an element forsupporting the head was damaged, an excessive load was applied to thedisk rotating driving motor and the disk could not be rotated. In casethat a height of the micro projection is more than several tens of nm,for example, a micro projection has 90 nm or more, the head friction islow and the head stickiness problem is not generated. However, it showeda poor head floating characteristic and showed an accident of headcrush.

Further, in case that the density of a micro projection is less thanseveral hundreds pcs/mm², for example, 110 pcs/mm², each of thepressures or the micro projections under the head load was high, asliding wear-out at the micro projections under a head load wasexcessive along with the times of a contact start-stops, a lubricantagent or carbon protective film was excessively damaged and a head crushwas generated at a value less than a contact start-stops of time ofabout 2000 to 3000. In case of a density of several tens of thousands ofpcs/mm², for example, 80000 pcs/mm², a contact area between the magnetichead and the disk surface was large, a head stickiness at the start ofthe contact start-stops operation occurred, an element for supportingthe head was damaged when the disk was rotatably driven with anexcessive load applied to the disk rotating and driving motor and thedisk could not be rotated.

In the above-described preferred embodiment, a method for forming themicro projection by using the grinding tape and some advantages invarious characteristics of the thin film magnetic disk having thissubstrate have been described. However, similar effects may be attainednot only in the grinding tape, but also in surface working processessuch as a cutting process, a grinding and cutting process, a lapping anda polishing and the like and additionally a surface processing methodsuch as an etching or a sand blasting process and the like or a dryprocess pattern forming method. In one preferred embodiment of thepresent invention, a width of the grinding tape is narrower than that ofa working surface of the disk, contact rollers pressing this grindingtape are reciprocated in a radial direction of the disk and the surfaceof the disk is worked while being oscillated. However, it may also beapplicable that a width of the grinding tape is approximately the widththe surface of the disk to be worked, or a grinding tape having a widthwider than that of the surface to be worked is used, oscillated in aradial direction of the disk or the disk is worked without anyoscillation to get a similar effect.

As another example of an application of the present invention, the diskworking method and the working device of the present invention wereapplied to a protective film surface of the thin film magnetic disk.That is, after the Ni-P plated disk of the substrate is textured, anon-magnetic base film, a magnetic medium and a carbon protective filmare sputtered, and during this process, some fine micro projections areadhered to the surface of the disk. So, it is necessary to remove themicro projections without influencing the base of the magnetic mediumand the like and to enable a setting of a minute pressing force to beperformed so as to make a smooth surface and further to always maintaincontrol of the minute pressing force. In view of this fact, it becomesnecessary to provide a disk working device using the grinding tape ofthe present invention.

Its practical example will be described later.

FIG. 22 is a graph for showing an output of the piezo-electric elementfor the case that a floating test was performed for the floating heightof the floating magnetic head having the piezo-electric element thereofof 0.15 μm before the thin film magnetic disk having Co-Ni magneticmedium and a carbon protective film sputtered on the substrate with anouter diameter of 130 mm and an inner diameter of 40 mm plated with Ni-Pand surface polished. FIG. 23 is a graph for showing an output of theabove-described piezo-electric element in case that the above-mentionedmagnetic disk is finished by the disk finishing and working device shownin FIGS. 1, 2a, 2b and 2c in the same manner as that of theabove-mentioned working method under a working condition in which thegrinding tapes 4a and 4b have a particle diameter of diamond of 0.5 μm,a pressing force of the rubber resilient contact rollers 8 and 9 againstthe magnetic disk 2 is 2N, the number of rotation of the magnetic diskis 1000 rpm and a reciprocating time of the working head is more thanfive times. As apparent from these graphs, the magnetic disk 2 beforefinishing work has an output of the piezo-electric element made by microprojection V having a height of more than 0.15 μm and to the contrary,the magnetic disk 2 after it is finished by the disk finishing andworking device shown in FIGS. 1 and 2 has no micro projection having aheight of 0.15 μm or more, so that it shows that the micro projectionhas been removed.

Further, as a method for making an accurate removing of the microprojection on the magnetic disk surface, positions of the contactrollers to which grinding tapes are added on the magnetic disk arealways detected by a linear scale arranged in the working headreciprocating means and the disk rotating motor is controlled so as tocause a relative speed between the grinding tapes and the disk surfaceto be always constant. Under this action, an influence of the dynamicpressure caused by some polishing agents present between the grindingtapes and the disk surface during the texture work is made uniform overan entire disk surface. Therefore, it is possible to perform an entirefinishing of the disk with a uniform pressing force and to have auniform effect of removing the micro projections as well as a highlyaccurate disk.

As described above, in case that the present invention is applied to theprotective film surface of the thin film magnetic disk, a minutepressing force can be uniformly applied onto the disk surface, so thatthe micro projections on the disk surface can be removed little bylittle and thus the micro projection can be made flat positively withoutdamaging the magnetic medium around the micro projection. Further, sincethe substrates of the grinding tapes 4a and 4b have diamond particlesadhered and held with a binder such as resin, if a quite high strikingforce is applied to the grinding tapes, this striking force can beabsorbed with the binder and soft contact rollers, resulting in that themagnetic medium other than the micro projection may not be damaged.

In regard to the grinding tapes applied in the present invention, it isnecessary to provide the grinding tapes having uniform cutting andgrinding particles in order to make an accurate formation of a microprojection, have a height of micro projection of several nm to severaltens of nm and a density of several hundred pcs/mm² to several tens ofthousands of pcs/mm² under a stable formation work.

A prior art grinding tape as shown in FIG. 24 is made such that finegrinding particles 65 are dispersed within resin 66, coated over apolyester film 67 and then heat treated, wherein its sectional shape haslarge uneven corrugations and its effective grinding particle cuttingblade contributed to the surface working is unstable. Due to this fact,the surface of the prior art grinding tape is made such that extremityends of the grinding particles on the surface of the grinding tape arecorrected uniformly by a truing and dressing of the grinding tape shownin FIG. 26 in such a way as one in which the disturbance in roughness atthe extremity ends of the grinding particles is less than 50 nm and aneffective acting grinding particle density becomes several tens toseveral hundred pcs/mm² as shown in FIG. 25. In addition, the truing anddressing processes for the grinding tape will be described in detail inreference to FIG. 26. A grinding tape 70 is taken up with a grindingtape take-up motor 74 while the grinding tape 70 is being held between adresser 71 having diamond particles fixed to its cylindrical surface anda roller 72 having a surface of back-up soft material. At this time, inorder to make a uniform tension of the tape, the grinding tape forcorrecting the surface is supported by an output shaft of the brakingtorque motor 74. Minute pressing force is applied to the dressor 71 anda piezo-electric sensor 76 is arranged at the rotary shaft of the roller72 in order to control the pressing force. With the grinding tapecorrection device, the grinding particle layer in the grinding tapesurface becomes flat, resulting in that a disturbance of the number ofthe effective acting grinding particles can be reduced and so anaccuracy of the micro projection at the textured surface can beimproved. A reference numeral 75 indicates another truing and dressingmethod for another grinding tape, wherein a so-called self-correctingtype dressing method is used in which the surface of the grinding tapeis slid with the same grinding tape surface to perform the dressing.Further, this reference numeral 75 denotes rollers for applying apressing force to the grinding tape having the grinding particlesurfaces to be pressed contacting to each other. Even with this method,the same result as that descriged above can be attained.

Due to this fact, the extremity ends of the grinding particles on thegrinding tape surface were uniformly corrected by the grinding tapetruing and dressing method shown in FIG. 26. A density of the microprojections could be controlled in a range of several hundred pcs/mm² toseveral tens of thousands of pcs/mm² by controlling a grinding particlediameter of the grinding tape and controlling the dressing condition ofthe grinding tape.

As described above in detail, according to the present invention, it ispossible to provide a disk working method capable of forming quite smallhighly accurate micro projections in a Ni-P plated substrate and anapparatus to be directly used in performing this method.

In the disk working device, the parallel leaf springs, strain guages anda pressing force correcting piezo-electric actuator are applied toenable the pressing force of the contact rollers against the disk toquite low and always be uniform, so that uniform micro projections whichare stable over an entire disk surface and the micro projections formedin the substrate plated with Ni-P are removed little by little, so thatthe micro projections can be highly and accurately smoothed.

Further, with the above-described disk working device, it is possible tocut the micro projections on the carbon protective film surface littleby little to make a positive removal of the micro projections and thereis no damage to the carbon protective film around the micro projectionsand a surface film of the magnetic medium. Therefore, a surface accuracyis ensured and a quite high smooth surface can be attained. As describedabove, according to the disk working device and its method of thepresent invention, micro projections having a height of several nm toseveral tens of nm are formed in the Ni-P plated substrate of themagnetic disk uniformly to have several hundred pcs/mm² to several tensof thousands of pcs/mm², resulting in that the head load is received bythe above-mentioned several micro projections in view of acharacteristic of a contact start-stops operation in which the magnetichead is intermittently contacted with the disk surface, a pressure ateach of the micro projections is reduced, and a deformation of the microprojections and its sliding wear is reduced. Further, deterioration ofthe protective film and lubricant film formed in the micro projection isless and its anti-sliding characteristic can be improved. Since theheight of the micro projections is several nm to several tens of nm,even if the head floating clearance is made small (for example, afloating clearance of 0.15 μm), there is no problem of striking themagnetic head and head crushing and further there is no problem of headstickiness caused by a lubricant film (coated less than a film thicknessof several nm) or a head stickiness caused by moisture contained in theatmosphere.

What is claimed is:
 1. A magnetic disk comprising a substrate coatedwith a magnetic film, a surface of the magnetic disk having microprojections with a bearing ratio curve providing a bearing ratio of 0.1to 10% at a depth of 5 nm from a highest peak of the micro projections,a relation between a height H of a peak of the micro projections from acentral line of a surface roughness curve of the surface and a depth Vof a groove from the central line of the surface roughness curve beingH/V≦0.5.
 2. A magnetic disk according to claim 1, wherein the height His in a range of at least 3 nm to at most 90 nm.
 3. A magnetic diskcomprising a substrate coated with a magnetic film, a surface of themagnetic disk having micro projections with a density of greater than110 and less than 80,000 peaks per mm², a relation between a height H ofa peak of the micro projections from a central line of a surfaceroughness curve of the surface and a depth V of a groove from thecentral line of the surface roughness curve is H/V≦0.5.
 4. A magneticdisk according to claim 3, wherein the micro projections have a bearingratio curve providing a bearing ratio of 0.1% to 10% at a depth of 5 nmfrom a highest peak of the micro projections.
 5. A magnetic diskaccording to claim 3, wherein said height H is in a range of at least 3nm to at most 90 nm.